Method and apparatus for relieving hobs



Get. 11, 1932. Q HEAD I 1,882,009

METHOD AND APPARATUS FOR RELIEV ING HOBS Original Filed Nov. 28. 1928 2 Sheets-Sheet 1 INVENTOR BY Ernent Cflaad r it;

ATTORNEY METHOD AND APPARATUS FOR RELIEVING HOBS Original Filed Nov. 28, 1928 2 Sheets-Sheet 2 I 4 INVENTOR BY Zrrzasl C. Head I I .1 TQRNEY Patented a. 11, 1932 tra STAT noonns'rnn, NEW YORK,"A conrona'r onon NEW YORK ERNEST 0. HEAD, or- 'nocnnsrnn, NEW. YORK, nssienon 'ro crimson wofaxspor -ME' 1HCD Am) AP ARAT S non BELIEVING Hons Original application filed November 28, 1928, LSeriaIvNo. 322,498. Divided "this applieation file d May 2 7,,1930.; Seria1 No.'456,21 5 1 1 1 The present invention relates to a method and to apparatus for relieving gear cutting hobs and particularly hobs for cutting spiral bevel gears.

This applicationis a division oifmylpending application, Serial No. 3223 98, filed N o ivember 28, 1928, covering a bob. 1

The primary purpose-of this nvention is to afiorda method of relieving hobs, such as are employed in the cutting of longitudinally curved tooth gears, which will produce ahob capable of cutting curved teeth on a gear which will mesh with the teeth of amating gear along a portion of their length only.

With the present invention, therefore, hobs can he made which are capable of cuttinglon- ,gitudinally curved tooth tapered gears that will mesh Witheach other with a properly localized tooth bearing.

Prior to this invention, hobbed gearshave lacked adjustment whenin mesh because, with previous-methods of hobbing, the tooth surfaces cut upon the two gears ofa pa r were of the same lengthwlse tooth shape and would match. each other along their whole leng th.

Such gears had, therefore, to beveryi accurately'and very rigidly mounted; As it is poss ble tocut longitudinally curved tooth tapered gears by other methods than a hobbing method and mismatch or localize the tooth beau ings, the inability to hob such gears with ya mismatch hasiheretofore been a serious drawback to the bobbing method. -Gears'without mismatch are unable to accommodate them-- selves to the inevitable inaccuracies of mounting and to the displacements under load which occur in commercial installations; The present invention enables this previous disadvantage to be overcome andpermits'of hobbing gears fully capable of accommodating themselves to variations in mountings or loads. 1

In the drawings: K

Figure 1 is a side elevation, partly in section, of a taper hobrelieved according to this invention; 7 c

Figure 2 is a diagrammatic view illustrating the preferred method of relieving this hob;

[Figure 3 isa fragmentary gpnn'Evi-w' of a lathe provided] with an attachment con- 'With therelieving of the tops ofthe'hob'teeth structed according to aipreferred ment of this invention adapted-to, relieve'hobs according to the methodjof thisinventiongfand Figure ,4 1s a fragmentary sectional view-1 the line of Figured I t V; l v 1 The present invention "relates only to the through this lathe andattachment, on

relieving of the' sides of the cutting teethof hobs. Thepresentinvention is not concerned and the tops oft'he teeth mayberelievedac cording to known practice or any suitable method. I I V 1By-mean's 'ofthe present p1'.ocess, hobs. are

ofa standardhob from a point midway the '7 length "of the hob towardbothfends thereof. I "lnaihobof constant pitch, this means -that ,[the' teeth willibe thinner midway the length -ofthe'hobjthan. at the endsofthehob. When a-hob relieved according to this invention employed to cut a tapered gear,, the thin1teeth p r I the hob will operate,midwayzthelength of the teeth. of the gear while the end" teeth of the "hob will operate ,on th ends of the teeth oft-he gear; f Thus tooth spaces. will be .cut on (the gearblank which arenarrower midway their length than attheir'endsand when such a gearis meshed with another gear lcut by-the same processor according to previ'ouspractice, it is obvious that-themating "tooth surfaces of the two gears willibeanor gg contact midway oftheirlength but bevou'tof contact at theirends. Theibearing or tooth contact willbe, in other,;words,l-localized.

L E'Lhepresent invention maybe applied to relieving of hobs ofieither variable 01- constant pltch, whether cylindrical ,or itapered, in fact, to any formjol' hob for cutting longitudinally curved tooth tapered gears. in a'speclfic aspect, the present invention has [for its purpose to improve the form of lhob produced by the ,relievingmethod of my pending application Serial No. M74311, filed .April 24, 1930, which is a division of'my pending application lS erialjjNo.:2-7 8,'208,filed 1928, andit isin connectionfwith aloo l various ways.

the improvement upon this prior invention,

of mine-that the present invention is illustrated.

By my prior invention, I have shown the advantage of relieving a taper, hob so'that its cutting edges are ofcontinuously'ch'anging pressure angle from one end of the hob to the other, as, with sucha hob, gearshaving tooth spacesandteeth of properly tapering depth can be cut. By means of the present in- 'vention, it is possible to improve my prior re.-

lieving process further in such way as to permit the production of a hob which will not only cut gears having teeth and tooth spaces of properly tapering depth but with a localized tooth bearing.

Thepresent invention may be practiced in According to the preferred embodiment, th-e relievin'g tool is swung in a circular arc asitmoves from one end of V the hob to the other during the relieving of the successive teeth of the hob, thereby feed- 1 ing therelieving tool inwardly as it moves from one end of the hob to the center thereof from hob. 7 As, stated, the present invention will be and' withdrawing the tool again as it moves the centertoward the other end of the describedin connection with itsapplication to the relieving process of my application No. 4 17 ,011 as affording a method for producing'a still further improved form of hob. In

relieving a hob according to the method of my pending application No. 447,011, the relieving tool is tilted continuously as it moves from one end of the hob tothe other to form cutting edges on the hob of continuously changing pressureangle from one end of the hob to the other. 10, lO a'nd 10f (Figure 2) show three positions of the relieving tool in relieving theteeth of a taper hob 30 by the process of my prior application No.

7 447,011. The relieving tool is "tilted continuously as it moves from oneendof the hob to the other so that the pressure angle a of thetooth 11 at the large end ofthe hob is less than the pressure angle a of thetooth 12 fat the small end of the hob. 'Due to the conpointed out in my prior application, this method of relieving'a taper hob results in'a' taper hob having teeth'at its small end which are of greater strength than the teeth of-taper hobs as. relieved by prior processes.

" Tn applying thexpresent invention to my prior process, not only is the relieving tool tilted as 'it-moves' from one end of the hob 5 to'the other, but it is fed first inwardly and then outwardly so that it cuts on different teeth of the hob at different depths with reference to the operating pitch surface of the hob, thereby causin someof the teeth of the vhob to be thinner t an others Preferably,

this feed is obtained by feeding the relieving tool along a circular are as it moves relatively from one end of. the hob to the other. Thus, the tipof the relieving tool is moved on a circular are 18 and any point 19 on the side surface of the tool m'ovesf'on an are,

parallel to the circular are 18. In the drawings the relieving tool is shown as positioned the tooth 11 at a point 23 lying in the conical surface 21 coaxial with the aXis22 ofthe hob.

As the tool moves from'one end'of thehob' to the other, the point 19 travels on the are 20, as described. Thus, the point19 will act at points 24, 24', etc., below the surface 21 during the relieving of the teeth 13, 14;, 15 and 16 and will again operate in the conical sur face-21 when it engages the tooth 12 at 23.

Thus, due-to its feed movement, the relieving tool will out at a greater depth on the teeth 13, 14,15 and 16, than on'the teeth'11 and 12.

so that the point 19 operates on one side of v 7 /11 di t fo -instance, as compared with 10, the distanoethe' relieving tool will h'ave'moved inwardly when it has reached the tooth 15; This movement will cause-adecrease of the amount indicated by the arrows at w in the thickness of the tooth meas- I 'ured 011 the surface 21. Asthe opposite sides ofthe hob teeth are relieved in a manne'r s milar to that illustrated it will be seen that a corresponding decrease in tooth thickness results during the relievingof the opposite side of the tooth 15." It will be seen, then, that as a result of the relieving method ofthis invention, the tooth 15' will be thinner'measured on the conical surface 21 or oniany conical surface coaXial wit-h the hob, than the end teeth 11 and 12 of the hob and it will be'understood that the teeth 13, 14 and 16 of-the hob will'also be thinner than the end teeth. 11 and 12 in proportion to their respective positions along the length of the hob and'the radius of the c are on which the relieving tool is swung. 7

When the hob blank is rotated at a uniform velocity and therelieving tool is moved at a uniform velocity in timedrelation with the blank rotation during the relieving of successive teeth of the hob, the lead of the hob will still remain uniform on the pitch line 21 despite the difference in thickness of its teeth measured on that line. Thus, as indicated in Figure 1, the distances p measured on the line 21 from the center of one tooth of the hob to the center of another tooth inthe same axial plane of'the hob are equal. The hob differs from the usualvtaper hob of constant pitch,

however, because its teeth are of changing thickness along the pitch line.

t indicates-thethickness measured on the surface 21 of the teeth 14 and 15, whichare equi-distant from a point midway the. length of the hob. This thickness 2? is less t-lran'the thickness 6 of the teeth 14 and 15 measured on this surface21 and the thickness 25' is-in turn less than the thickness t of the-teeth '12 measured 011 this same surface.

In the hobshown, thethickness ofthehob teeth is uniform on the line 20, but onany parallel arc, due to the tilting motion of the tool informing thesidesofthe hob teeth so that their pressure angles change from One end of the hob to the other, there ls'a variation'from absolute uniformity of tooth thickness: l r y We have, then, as a res'ultof-the relieving method of thisinvention, a hob whose teeth are of varying thickness along'the conlcal surface 21 or any conical surface "coaxial with thehob axis 22. It will be readily'apparent that when such a hob is in operative relation with a tapered gear blank withaconical surface of the hob tangent to the pitch-cone suriace oi the gear and with the axis ofthe hob extending diagonally of the face of the blank, the hob will cuttooth spaces on the gear which are narrower midway their length than at their two ends. So the teeth of a tapered gear cut with a hob relieved according to thisinvention will be wider midway their length than at their ends and when the gear is meshed with a mating gear cut in the same wa-yor according to previouspractice, the teeth of the two gears willcontact along a portion of their length only, thus having the desired localization oi hearing .which enables the gears to accommodate themselves to the variations in mounting in practice. L r V Figures 3 and 4 illustrate apreferred form of apparatus for producing a hob according to this invention and in particularfor proand load which "occur 'duoing a hob which has thecharacteristics of thehob described in my PllOlfPQlldll'lg ap plication No. 447,011. This apparatus is in the form of an attachment for a conventional form of lathe. I

designates the bed of the lathe, 26 and 27 the head-stockand tail-stock centers, respectively, and 28 the driving dog. The work,

that is, the hob 30 to be relieved, is mounted between the two centers and is rotated continuously during the relieving operation by the head-stock driving mechanism of the lathe. 32 indicates the lathe carriage which mounted for sliding movement upon ways 33 formed on the bed 25 of the machine.

Secured "to the carriage 32 isan. apron 34 which carries a nut 35 that engagesthelead screw 36 of the lathe. his lead screw 36 may be driven in'timed relation with the r0- tation of the head-stock spindle in the usual or in any other suitable manner.

' The carriage 82 carries the relievingattachment of this invention, w

carrier 42 serves as a .ing slide 44.

Mounted? on thecarriage32zfor angular'adustment thereon is :a p

circular shape.

acarrier42 which is guided in its reciproate. 38 of generally. This :plate 38 is provided with an annular flange 39 that seats in a circular groove or socket provideditherefor in the upper face of the carriage 32. i

. Reciprocably mounted upon the plate 38 is eating movement .on the plate by suitable guide ways which engage corresponding g-uide surfaces formed .o'nthecarrier. -The supportlfor the relie v- The relieving slide 44. carries a slide 45 which is, adjustable on theslide 144 by means ;of the screw 46 and nut47. Mounted on the slide 45 is another slide 48 which is adjustable, on the slide 45. in a direction at right Jangles toithe direction-of adjustment of the slide 45. The adjustmentot the slide 48 is accomplished by means of ascrew 49 which threads into anut (not shown) which is secured to the slide 45.

Mounted on'theslide 48 for pivotal movementthereon is a tool block or support 50.

Why means of the straps 52 and bolt-53.

. The pivotal movement of the support takes place aboutthe axis of a stud 55iwl1ic'h is j ourn'aledin the slide 48. y

The relieving motion is imparted to the] relieving tool 51-through reciprocation, of

the slide 44by means of the snail-cam 60. This cam engages a contact memberfil which is secured to an extension of the slide 44. The

cam is rotated in timed relation-With the rotation of the head-stock spindle andot the lead screw 36, being drivenfrom the horizontal shafti62 through a pair of miter gears 63 and 64, the vertical shaft .65 which is l :journaled inthe carriage 32,'the-miter gears 66 and 67 the latter of which has asplined connection with the'horizontal shaft 68 which isjournaled in the angularly adjustableplate 38and in'the carrier 4.2,and the'bev'el gears 69 and .70, the latter of which is secured to the vertical shaft 71 to which'the camel) is fastened." Any usual 'or suitable form of gearing may be employed for. maintaining the timed relation between the various operating parts ofthemachine. An example of one form of such gearing is illustratedin my co-pendin'g application above mentioned.

As'the work rotates and the carriage .32 moves longitudinally on'thebed 25 andthe cam. 60 imparts the relieving movements 1 to the'relieving tool 51,- therelative feed'move- -ment which constitutesthe novel feature of this invention is produced; :The mechanism for. producing this feed movement will now be described. i

- Secured to thebed orfra-me' 25-at oneside thereof is v a bracket 17 2. Mounted on this bracket 7 2 for "angular adjustmentthereon .is a guideplatei73, The guidepl-ate 73.is prosocket or recess formed in the extension 76 of the carrier. 42; The follower 77. is suitably vided with an integral stud 7 4t whichis journaledina'suitablesoeket or recess formed in I the bracket :72. The guide plate-is formed I v:circular arc. Pivotally-connected to an 6X. tension 7 6 formed'on the carrier42is, a,fol-

. for taking up wear.

with a-guide way 7 5 which is of dove-tailed shape in crosssection and, in the preferred embodiment, is curved longitudinally on a lower 77 The-follower 77 is provided with a pivot pin .78 thatflengages in a suitable shaped to engage the guide-way 75 of the guide plate 73 and a gib 79 maybe provided If a: cylindricalhob is to relieved, the

guide plate is ordinarily set in zero position sothat the median line of the guide way 75 is parallel to the aXisof the work. 'VV hen a taperhob is tofbe relieved,the guide plate 73 is adjusted angularly on the bracket 72 preferably to an angle corresponding to the pitch cone angle of the hob. The bracket 72 is,pro vided with agraduated flange 80 and the guide plate 7 3 with an index mark readable against the graduations on the flange 80 so that the guide plate canbe set accurately in the required position. It is secured in any theguide plate and thread into the bracket .72.-, It will be seen that as the carriage 32 7 .moves longitudinally on the bedof the machine, the guide plate-73, through the guide lieving toolmoves from'the'center tothe I :ence to Figure The radius of curvature,

usted position bymeans of bolts 82 which pass through the arcuate'slots 33 formed in way 75 and follower 77, will'cause thecarrier 38 to .be moved inwardly 'asthe relieving tool movesfrom'o-ne end of thethob to the center thereof and then outwardly as the reother end of the hob. This is due to the arouateshape of the guide rail. The movement of the relieving tool inwardly andthen outwardly effects the required. feed movement, causing the thickness of the teeth of the hob to be varied, as'already described with referin fact, the general shape of the guide way 75 r 3 and 4. I g

tilting motion ofthe relieving tool isthe same.

the hob relieved by the'method of this in ing method described in my application No.

447,011. I have so shown it inthe present application, both in Figure 2 and in Figures The mechanism for producing the that shown in my'prior application and reference may be had to that application for a more complete description thereof. 'This mechanism will be only briefly described here; The tiltingmovement of the relieving tool iseffected'by angular movement of the support 50 about'the axis of the stud55. 'When one side ofothe teeth of the hobi is being relieved, the arm-85 is connected to the support 50 by engaging the opposed clutch teeth formed on the arm and the support 50 and clamping these-teeth in engagement by threading up on the nut 87"which engages the'stud 55. "The'arm 85 carries at its outer end a stud, 89 on which is mounted, a roller that is adapted-to engage the vertical surface of aguide rail 90 which is secured to the carriage .32. It will beseen that asthe tool slide 44 reciprocates under actuation of the cam 60, the tool support 50 will be rocked by reason of engagement of the roller carried by the arm'85 withthe guide rail 90. Hence,

as the relieving tool operates to relieve the 7 side surfaces of each of the teeth of the hob,

it"will be tilted,causing the pressure angle of the teeth of the hob to be varied continuously from front to rear. The; effect of this is to form teeth on thehob which will have the same cutting action after sharpening as when new, as fully described in the two applications above mentioned. It will be seen, moreover, that asjthe carriage 32 moves longitudinally and the carrier 42 is actuated by reason of the enga ;ement of the follower 77 with the guide rail 7 5, the relieving tool sup port 50" will have a continuous tilting motion, r

producing a change inpressure angle of the cutting edges of the hob from one end of the hob to the other. 'lVhen this change is such asto cause an increase in the pressure angles of the'cutting edges as they approach the small end of the hob, the teeth at the small end ofthe hob will be stronger than inprior constructions, as clearly pointedoutin the application above "mentioned.

V V TvVhere the relievingmotion is being soeffected, as just described, to produ'cefteeth on the hob of changing pressure angle from front to rear with cutting edges of changing pressure angle from one end of the hob to the other, in relieving the side of the hob teeth opposite to that shown in Figure 3, the arm ,85 is taken offof the. attachment and an arm 92, shown in-dotted lines, substituted therefor. This'arm' 92, like the arm is secured to the rocking support 50 and carries its, outer end a roll-erwhichengages with the vertical guide surface of a rail 93 which is secured to the carriage 32 at a point diagonally opposite the pointat which the guide rail is secured The operation of the'arm' 92 and the roller carried thereby is similar to that of the arm 85 and its roller. .As the relieving slide 44 reciprocates, the relieving tool is tilted and. this tilting motion is continuous from one end of the hob to the other due to the motion of the carriage- 32 which causes a movement to be imparted to the carrier 42 by reason ofthe engagement of" the follower 77, which is secured to the carnor, with the guide rai175. i

The operation of the attachment shown will'be understood from the preceding description but may be briefly summed up here.

' The slides 45 and 48 arev firstadjusted in accordancewith the diameter and pitch of the hob tobe relieved and the plate 38 is adjusted angularly on the carriage 32 in accordance with the pitch cone angle of the hob to be relieved. By means of this last adjustment, it is possible to positionthe relieving tool 51 so that it operates in a direction substantially perpendicular to the cone surface of the hob, thereby avoiding any possible.

slippage between the cutting edge of the tool and the teeth being relieved. The plate 73 is, also, adjusted angularly on the bracket 72 in accordance with the pitch cone angle of the hob. The curvature or conformation of the guide way 75 of this plate 73 is selectedin accordance with the changes which it is desired to effect in the standard thickness of teeth of the hob which, of. course, is governed by the amount of localization or concentratlon of bearing which it 1s desired to produce on the teeth of gears cut with the hob. One or other of the arms or 92 is secured'to the tool support 50 depending upon which side of the hob teeth is to be relieved.

When the machine is started up, the headstock center 26, the lead screw 36 and the cam 60 will rotate in timed relation. Thus, as the work rotates, the carriage 32'moves longitudinally and the cam .60 imparts relieving movement to the relieving tool; As each tooth of the hob rotates under the relieving tool, the'tool is fed inwardly by means of the cam 60 andas soon as the tooth clears the tool, the tool is returned ing the movement of the relieving slide 44, the I tool is tilted continuously by reason ofthe engagement of the roller carried by the arm.

85 or 92 with the guide surface or 93 as the case may be. This tilting movementof'the tool produces, as already stated, side'tooth surfaces on the teeth'of the hob which are of changing pressure angle or inclination from front to rear. i

As the carriage 32 moves longitudinally,

carrying the tool into position for engagement with successive teeth of the rotating hob blank, the angle of inclination of the cutting edge of the relieving tool with reference to the axis of the hob blank is changed continuously due to the feed movement imparted to the tool by the movement of the carrier 42 under actuation of the guide rail 75 and follower 77 This continuous tilting move-y ment of the tool acts, as above described,to

produce cutting edges .on successive teeth of the hobwhichare of continuously varying pressure angle from one end of thehobto the 3 other. Simultaneously,th e relieving tool receives a feed movement I inwardly and then outwardly, on the arc of a circle, if an arcuate guide 75 is employedas shown in Figure 3, This causes the relieving tool to cut deeper on certain teeth of the hob than on others, as

clearly illustrated in Figure 2, the point 19 in the cutting edge of-lthe hob traveling, for

instance, on the circle 20. The guide rail 75.v

serves, also, to maintain the relieving tool in operative relation with the successive teeth.

of the hob despite the taper of the hob, since the guide rail is disposed at an angle to the v axis of thehob corresponding to thepitch cone angle of the hob.

' l The Springs 99 w i ounted upon :1 .rods 100 that are secured in the carrier 42 and:

slide in lugs lOlformed on the angularly adjustable plate 38, serve to absorb any tendency toward vibration of the carrier 42 during its movement under actuation of the guide rail 75 and follower 77 andthey serve,,also, to.

return the carrier 42 to original positionduring the return movement of the carriage 32. A

Alever arm which is pivoted on astud 9 106 secured in the carrier 42, is provided to Q permit disengagingthe contact piece 61 from the cam 60 during'the return movement ,of

the carriage 32. When the lever arm is swung outwardly from the position shown in Figure 3, its nose l07 engagesthe head 1080f a screw, threaded into the relieving slide 44 and disengages the contactpiece 61 fromthecam 60. l/Vhile I have. described my invention in connection with a specific embodiment, it will '1 be understood that ltf lS capable of Vii-IlOllS further modifications without departing from its scope and that this application is ill-- tended to cover any adaptations, uses, or

variations of my invention, following, in gen-.1 eral, the principles ofthe invention and ineluding such departures from the present disclosure 'as come within known orcustomarypractice in the art and as maybe applied to] the essential features hereinbefore set forth; and as fall within the scope of the invention or;

the limits of the appended claims.

Having thus described my invention, what Iclaim is:

1. The method of the hob blank on its axis and movingthe re lieving tool and blank relative toone another to cause the relieving tool to follow-thehob thread, and producing. an additional "rel forming ahob which comprises 'eifecting a relative relieving movement between the hob: blank anda relievingtool for each tooth of thehob while rotating ative movement between the tool and blank,',

separate from the relieving movement, of; advanceand recess on relativeto the axis off ing toolfor each tooth of the hob while rotat-,

' ing the h'ob' blank on its axis and moving the relieving tool and blank relative to one another from' one end of the blank to the other along acurved line to cause the relieving tool to followthehob thread and produce teeth on the hobof varying thickness along the operating pitch surface of the hob.

' 3. The method of forming a hob which comprises'elfecting a relative relieving movement between the hob blank and the rlieving tool for each tooth of the hob while rotating the hob blank on its axis and moving the relieving tool and blankirelative to one another to cause the relieving tool to follow g the hob thread; While tilting the tool angularly as it moves from one end, of the hob tothe other to cause thetool to produce cutting edges on theteeth of the hob changing in pressure angle from one end of the hob to the other, and producing an added relative move ment betweenthe relieving tool andblank to cause the relieving tool to cutdeeperrelativeto the pitch surface of the hob on certain teeth of the hob than on others.

14. The method of relieving the side faces of-theteeth of a hob which comprises producing a relative relieving movement between the relieving tool and the hob blank for each tooth of the-hob while rotating the blank inga relative relieving movement between the 'on its axis and, producing a relative movement between the relieving tool and-blank longitudinally of the blank in which the tool is moved relative to the blank on'a circular arc. i

5. :The method of relieving the side faces of the teeth of a hob which comprises producrelieving tool and thehob blank for each.

tooth of the hob while rotating the blank on its axis at a uniform velocity and producing a relative movement between the tool and the blank at a uniform velocity in a direction longitudinal of the hob and simultaneous-' ly producing a feed movement between the tool and blank during the last named movement to causethe relieving tool'to form teeth on the blank of varying thickness along the operating pitch surface of the-hob.

6. Themethod of relieving the side faces of the teeth-of a hob which comprises pro ducing' a relative relieving movement be tween the relieving tool and the'hob blank for each tooth of the hob while rotating the blank on its aXis at a uniformivelocity and producing; a relative movement between the tooland blank at a uniform velocity in direction longitudinal of the hob and simultaneously feeding the tool inwardly and then outwardly relative to the'blank as the tool moves from one end to the center of the blank andthen to the other endthereofduring the last named 'relative movement.

7. The method of relieving the side faces of the teeth of a hob which comprises pro-- ducing relative relieving movements between the relieving tool and the hob blank while rotating the blank on its axis at a uniform velocity and p-roducinga relative movement between the tool and blank at a uniform velocity in a directionlongitudinal of the hob and simultaneously moving the relievmg tool bodily along a circular arc relatlve to the blank during the last named movement. a v I 8. The method of relieving the side faces of the teethof a taper-hob which comprises effecting a relieving movement between the relieving tool and hob ina direction inclined to the cone surface of the hob while rotating the blank on its axis and producing a rela-' tive movement between the tool and blank in a direction longitudinal of the hob during which the. tool is fed "relative to the hob blank to produce teeth on the hob of varying thickness along a conical surfacecoaxial with the aXis of the hob blank. 7 I v 9. Themethod of relieving the side faces of the teeth of a taper hob which comprises effecting relieving movements between the relieving tool and hob blank in a direction inclined to the cone surface ofthe hob-while rotating the blank on its aXis at a uniform between the tool blank at a uniform velocity in a direction longitudinal of the hob during which the tool is' fed relative to the blank to "produce teeth on the hob of velocity and producing a relative movement varying thickness along aconical surface 00- r axial with the hob.

10. The method of relieving the side faces of the teeth of a taper hob which comprises effecting relieving movements between the relieving tool and the hob blank in a direction inclined to the, cone surface of the blank while rotating the blank on its axis and producing a relative movement between the tool and blank in a direction longitudinal of the blank during which the relieving tool is fed inwardly toward the axis of'the blank as it 'moves from'one end of the blank to the cen-' ter thereof and is then withdrawn outwardly as it moves from the center to the other end thereof.

' 11. The method of relieving the side faces of the teeth of a taper hob which comprises 7 effecting relieving movements between the relieving tool and the hob blank ina direction inclined to the cone surface of the blank while rotating the'blank on its axis, at a uniform velocityfand producing a relative movement between the tool and blank at a at different uniform velocity in a direction longitudinal of the blank during which the tool is fed inwardly toward the axis of the blank as it moves from one end of the blank to the center thereof and is'withdrawn outwardly as it moves from the center'to the other end of the blank.

12. The method of relieving the side faces of the teeth of a taper hob which comprises effecting relative relieving movements between the hob blank and the relieving tool in a direction perpendicular to the cone surface of the blank while rotating the blank on its axis at a uniform velocity and prof, ducing a relative movement between the hob and blank longitudinally of the blank at a uniform velocity and simultaneously moving the relieving tool bodily relative to the blank on a circulararc to cause the relievmg tool to out at varying depths as itmovesfrom one end of the hob to the other.

13. The method of relieving a taper hob which comprises producing relative reliev ing movements between the hobblank and the relieving tool to relieve the side faces of the teeth of the blank and, while rotat-- ing the hob blank on its axis and simultaneously producing a relative movement between the blankand the relleving tool longitudinally of the blank and a continuous feed movement between the hob and blank in one direction as the tool moves relativelyfrom one end of theblank to the other, tilting the relieving tool continuously as, it moves from one end of the blank to the other and simultaneously producing asupplemental feed movement or tnetool to cause the tool to move inwardly as the tool moves from the center to one: end of the hob and outwardly as the too-lmoves from the'center to the other end of the hob.

14. In apparatus for relieving hobs, a tool support, arotatable work support, a carriage 011 which one of said supports is mounted,

means for producing relative relieving move- 7 a work support journaled in-the bed, a carriage mounted on the bed for movement axially of the work support, a carrier slidably mounted on the carriage, a slide adjustable angularly on the carrier and reciproca-ble thereon, atool support mounted on the slide,

means for rotating the work support, means for effecting movement of the carriage,

means operated by movement of the carriage for effecting a movementoff advance and recession ofrrthe carrier relative to-the work support, and means for reciprocating the slide to impart relieving movements to the" i 16. In apparatusfor relieving h0bs,,a bed, a worksupport journaled on thebed', a car.- ria-g'e mounted on the bed for movement aX- ially ofthe work support, a carrierslidable onthe carriage, a slide reciprecable on the carrier, tool support mounted on the slide, means for rota p for efleetingfmovement of the carriage, means operated by movementiofthe carrier for effectinga movement of advance and rethework support, means cession ofthe vcarrierrelative to the work,

.support,. and means for reciprocating the slide to impart reliev ng: movements 'to the" I 17. In amachine for relieving hobs, abed,

a'carriage mounted on the bed for movement 7 longitudinallythereon, a tool supportanda work support, one of which is mountedon the bed and the other on the carriage, means for rotating the work support, means for effecting movement oftlie carriage, means for pri'iducing relative relieving movements between the tool and work supports during the before-mentioned movements, and means operative on movement: of the carriage for producing a movement 'ofapproach and recession between the tool and work supports as the toolmoves relatively longitudinally of the work." i i 7 18. In a machine for-relieving hobs, a bed,

a carriage mounted on the bed for movement longitudinally thereon, atool support and a work support, oneof'which is mounted on the bedan'd the other on said carriage, means for rotating" th 7 work support, means for effecting movement of said 'carria e, means for producing relative relieving movements between the tool and' work sup'ports during the before-mentioned movement, a carrier on which one of said supports is mounted, acontrol member secured tothe'bed' and. having a guide surface curved longitudinally with reference to the directionkof travel of the carriage, and means operatively connecting the carrier with the control member whereby, on movement of said carriage, said carrier is moved transverselyef the direction of movement of thecarriage to cause a move ment of'relativeapproach and recession between the tool and work supports as the carriageinoves on the bed.

' 19'. In a machine for r a carriage mounted onthebedfor movement longitudinally thereon, a tool support and a work support, one of which ismounted on the bed and the other on said'carriage, means for rotating the work support, means for efi'ectingim'ovement of the carrier, means for producing relative relieving'movements believing hobs, a bed,

iao

tween the tool and work supports, during the before-mentioned movement, means operative on movement of the carrier for producing a movement of approach and recession between the tool and Work supports as the tool moves relatively longitudinally of the work, and means whereby the movement of the carriage causes the tool support to be tilted, as the carriage moves on'the bed and during the relieving of each tooth of the hob,

to cause the tool to form teeth on the hob With cutting edges of changing pressure angle from one end of the hob to the other and with side faces of changing pressure angle from front to rear. 7

20. In apparatus for relieving hobs, a tool support, a rotatable work support, a carnage on which one of said supports is mounted,

, means for moving the carriage longitudinally of the work, means for rotating thework support on its axis, means for lmparting relative relieving movements between the tool support and work support in timed relation to the work and carriage movements, and means for simultaneously moving the tool 1n a clrcular V are as it is moved longitudinally of the work the carrier and adapted to engagesaid guide surface for- 1mpart1ng a feed movement to 40 said carrier asthe carriage moves'longitudinally, means for actuatlng the carnage.

for inoving tlie carriage longitudinally of the Work, means for imparting relieving movements to the tool in timed relation to the work and carriagemovements, means forfeeding the .tool vsupport inwardly and then outwardly as the tool moves from one end of the work to the other, and means whereby the movement of the carriage acts to'change the inclination of the side cutting edge of the tool to the axis of the work as the tool movesffrom one end'ofthe work to the otherf. r

24. In apparatus for-relieving taper hobs, a bed, a reciprocable tool slide, a rotatable work spindle, a carriage movable longitudinally of the work, atool support 'rotatably mounted on the slide and adapted tocarry a relieving tool, a carrier uponwhich the slide is reciprocable, a plate upon which the carrier is movable, said plate being mounted on said carrier for angular adjustment thereon. to position the tool slide and carriage; for movement in a direction perpendicular to the cone surface of the work, an angularly adj ustable guide member mounted on the bed and having an arcuatem'uide surface,a' follower secured to said carrier adaptedto engage said i guide surface,; means for rotating thework spindle on its axis, means for imparting movement to the carriage, means for reciprocating the tool slide, a second guide ment her mounted on said carriage, and a follower secured to the tool support adapted to engage said second guide member whereby moves 1 ment of the tool carriage acts'to move the tool support continuously during movement of the carriage to change the inclination of the side cutting edge of the tool continuously relative to the axis of the work as the tool moves from one end ofthe work to the other ERNEST C. HEAD.

means for reciprocating the tool slide to impart relieving movements to the tool, and

means for rotating the workspindle on its axis.

22. In apparatus for relieving hobs, a tool support, a rotatable work support, a carriage upon which one of said supports is mounted, means for moving the carriage longitudinally of the work, means for rotating the work support on its axis, means for imparting a relative relieving movement between the tool support and'the work support in timed relation to the work and carriage movements,

' means for moving the tool inwardly and then outwardly as the tool movesfrom one end of the work to the other, and means for simultaneously changing the inclination of the side cutting edge of the relieving tool relative to the axis of the work as the tool movesfrom one end of the. work to the other. 7 V r 23. In a machine for relieving taper hobs, a tool support, a rotatable Work support, a' carr age upon which one of saidisupports is mou'nted,-means for rotating the work, means 

